This application is based on and incorporates herein by reference Japanese Patent Applications No. 2000-19302 filed Jan. 27, 2000 and No. 2000-387270 filed Dec. 20, 2000.
The present invention relates to an engine control unit, and particularly to an engine control unit which changes input clocks depending on presence/absence of failure in a crank signal system.
An engine control unit (ECU) is an electronic control unit for performing controls such as fuel injection control, ignition control, and idle speed control to operate an engine in an optimum state. Specifically, signals from various sensors for sensing engine operating states such as crank angle and engine coolant temperature are supplied to the ECU to control an optimum fuel injection amount, injection timing, ignition timing, and the like.
Controls synchronized with the engine speed such as ignition control and injection control, that is, controls synchronized with a crankshaft rotation position, are performed by generating a signal of ignition pulses or the like after elapse of offset (delay) time from a predetermined crankshaft rotation position indicated by the edge of a crank signal.
It is, however, necessary to perform an arithmetic operation for converting the angle to time. There is a demand for reduction in processing load and improvement in accuracy.
It is therefore an object of the present invention to provide an engine control unit with reduced processing load and improved accuracy and, moreover, capable of properly controlling the engine even when a crank signal system fails to generate crank signals properly.
According to the present invention, a crank signal of a pulse train of a predetermined angle interval corresponding to rotation of a crankshaft of an engine is generated and its pulse interval is measured. Frequency multiplication signals of integer times of the crank signal are generated as angle clocks by using the measured pulse interval. The angle clocks are used to determine a time point of fuel injection and/or ignition events of the engine as long as a crank signal system supplies the crank signal properly. When a failure in the crank signal system is detected, time clocks are used in place of the angle clocks to determine the time point of fuel injection and/or ignition events.